Email

We offer no support for email whatsoever including settings, delivery/spam and so on.
Usefull tools:

https://mxtoolbox.com/

https://www.mail-tester.com/

https://isnotspam.com/

https://spamscorechecker.com/

https://www.port25.com/support/authentication-center/email-verification/

See DNS

How to sent mail to mail-tester via WordPress

Example given that your test mail address is "test-thisissomerandom@srv1.mail-tester.com" and your site is "site.com".

OPEN
wp-config.php

FIND
require_once ABSPATH . 'wp-settings.php';

AFTER, ADD NEWLINE

if( isset($_GET['mailtester'] ) ) {
    wp_mail( 'test-thisissomerandom@srv1.mail-tester.com', 'test', 'testbody' );
}

DIY
visit: https://www.site.com?mailtester=true

visit the mailtester URL and apply fixes

Now, retest
Once you are done *remove* the 3 lines from your wp-config.php

if( isset($_GET['mailtester'] ) ) {
    wp_mail( 'test-thisissomerandom@srv1.mail-tester.com', 'test', 'testbody' );
}